1. Field of the Invention
The invention relates to cartilage implants for skeletal joints.
2. Description of the Related Art
Adjacent bones of the skeleton form connections called joints. These joints typically include one or more types of cartilage to reduce friction and impart flexibility. Hyaline cartilage, also known as articular cartilage, covers the joint surfaces of the bones and presents a smooth, slippery surface which facilitates the smooth relative motion of the bones. Hyaline cartilage has some elasticity and may provide some cushioning of percussive loads on the joints.
Fibrocartilage is an extremely resilient tissue and is also present at skeletal joints. In some joints, it provides great strength while allowing some movement as in the intervertebral disks and in the interpubic joint. In freely movable joints, where the surfaces are completely separated, the bones forming the joint may be separated by fibrocartilaginous plates or menisci. Menisci are found in the temporomandibular, stemoclavicular, acromioclavicular, wrist, and knee joints. The menisci fill the gap between the opposing bones at various positions of their articulation, increase the depth of engagement of the articular surfaces to increase joint stability, ease gliding movements, distribute joint pressure, and attenuate shock to the joint.
For example, the meniscus of the knee joint is a half moon shaped piece of cartilage that lies between the weight bearing joint surfaces of the femur and the tibia. It is triangular in cross section and is attached to the lining of the knee joint along its periphery. There are two menisci in a normal knee; the outer one is called the lateral meniscus, the inner one the medial meniscus. The menisci play an important role in absorbing impact loads. Complete removal of a meniscus can result in progressive arthritis in the joint.
The various cartilages of the joints are subject to damage due to traumatic injury, aging, and disease. Various repairs and replacements have been used to relieve pain and restore function to the joint where the cartilage has been damaged. For example hyaline cartilage may be damaged by impact injuries or worn down in the course of arthritis. Typically, the ends of the bones forming a joint are cut away and replaced with prosthetic bearings made of metal and plastic to restore pain free articulation of the joint. In cases where the damage occurs as a small localized defect, some investigators have attempted to replace only the small defect by placing a patch of replacement material, natural or synthetic, at the defect.
Fibrocartilage is often damaged by traumatic motion injuries such as automobile accidents and sports and job related injuries. For example, tears to the meniscus of the knee often result from a sudden load being applied to the meniscal tissue which is severe enough to cause the meniscal cartilage to fail and let go. This usually occurs from a twisting injury or a blow to the side of the knee that causes the meniscus to be levered and compressed against the bone. However, fibrocartilage may also be damaged due to degeneration. For example, degenerative meniscal tears are a failure of the meniscus over time. There is a natural drying out of the meniscus that progresses with age. The meniscus becomes less elastic and compliant and as a result may fail with only minimal trauma including during activities of daily living such as squatting and bending. Fibrocartilage repairs include suturing or replacement of the damaged tissues.